1. Field of the Invention
This invention relates to a tool positionable in a drill string or stem which is useful for absorbing shock, vibration and impact loading otherwise imparted to the drill string during drilling operations.
2. Description of the Prior Art
When a well is being drilled, the vibration caused by the drill bit is substantial. In some cases, the vibration frequency caused by the drilling can reach the harmonic frequency of the drill string, which causes the drill bit to begin bouncing off of the bottom of the hole. This condition is called slip-stick. This condition is completely undesirable, and is harmful to the drill bit and the other tools of the drill string. These tools include such equipment as the mud motor, the MWD Tools (Measurement While Drilling), and the LWD Tools (Logging While Drilling), just to mention a few. Slip-stick can also reduce penetration rates, which adds to the over all cost of drilling a borehole.
Because of the above noted problems, a number of prior art references exist which show various forms of vibration dampening and shock absorbing devices for incorporation into the drill string. By way of example, U.S. Pat. No. 4,162,619, issued Jul. 31, 1979, to Nixon et al., shows a shock sub for a well drilling string having a tubular housing adapted to be connected to one part of a drill string and a mandrel extending longitudinally into the housing and having an end portion adapted for connection to another part of the drill string. The mandrel and housing are shaped to define a non-circular annular cavity there between when assembled together. A compressible elastic metallic spring means is positioned in and substantially fills the non-circular annular cavity and is compressible longitudinally, radially and circumferentially to absorb longitudinal, radial and torsional vibration and impact loads and to transmit rotary movement between said housing and mandrel for imparting rotation from one part of the drill string to the other part connected by the drill sub. The spring means is preferably a knitted wire fabric or rope compressed into a compact mass capable of spring deflection in longitudinal, radial and circumferential directions relative to said shock sub assembly.
U.S. Pat. No. 4,211,290, issued Jul. 8, 1980, to Mason et al., shows a drill string tool having a low spring rate deformable element and a relatively long stroke. The deformable element comprises a stack of alternating non-deformable washers and deformable elastomer rings extending throughout the length of the element chamber. The element washers and rings are substantially out of contact with the side walls of the mandrel and barrel, so that each segment of the element experiences the total shock load. The spline and deformable element are in an oil bath. The annular space between mandrel and barrel is sealed at the upper end by a fixed seal and at the lower end by a floating seal.
The several forms of vibration dampeners and shock absorbers known in the prior art all suffer from one or more deficiencies.
The foregoing examples of the related art and limitations related therewith are intended to be illustrative and not exclusive. Other limitations of the related art will become apparent to those of skill in the art upon a reading of the specification and a study of the drawings.